Global reach, higher impact
Epigenetic mechanisms in UM
Potential therapeutics targeting...
Int J Biol Sci 2017; 13(4):426-433. doi:10.7150/ijbs.18331
Role of Epigenetics in Uveal Melanoma
Department of Ophthalmology, Ninth People's Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, People's Republic of China
This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/). See http://ivyspring.com/terms for full terms and conditions.
How to cite this article:
Li Y, Jia R, Ge S. Role of Epigenetics in Uveal Melanoma. Int J Biol Sci 2017; 13(4):426-433. doi:10.7150/ijbs.18331. Available from http://www.ijbs.com/v13p0426.htm
Uveal melanoma (UM) is a severe human malignancy with a high mortality rate that demands continued research into new and alternative forms of prevention and treatment. The emerging field of epigenetics is beginning to unfold an era of contemporary approaches to reducing the risk and improving the clinical treatment of UM. Epigenetic changes have a high prevalence rate in cancer, are reversible in nature, and can lead to cancer characteristics even in mutation-free cells. The information contained in this review highlights and expands on the main mechanisms of epigenetic dysregulation in UM tumorigenesis, progression and metastasis, including microRNA expression, hypermethylation of genes and histone modification. Epigenetic drugs have been shown to enhance tumor suppressor gene expression and drug sensitivity in many other cancer cell lines and animal models. An increased understanding of epigenetic mechanisms in UM will be invaluable in the design of more potent epigenetic drugs, which when used in combination with traditional therapies, may permit improved therapeutic outcomes.
Keywords: Epigenetics, Gene Therapy, MicroRNA, DNA Methylation, Uveal Melanoma.
Cancer is defined as uncontrolled cell growth and the acquisition of metastatic capacities. There are various mechanisms by which these cellular changes occur. The typical mechanisms are mutation, chromosomal deletion or translocation, and dysregulated signaling pathways. These events may activate genes that promote uncontrolled cell cycling or inactivate apoptosis. Uveal melanoma (UM) is the second most common form of human melanoma and the most common primary intraocular malignant tumor in adults, with an annual incidence of 6-7 cases per million per year [1, 2]. According to the Collaborative Ocular Melanoma Study group (2001), about 50% of UM patients will develop liver metastasis within 10-15 years of enucleation . Early metastasis leads to the high death rate associated with UM .
The characteristic processes associated with UM generation are well described in the existing literature, and numerous comprehensive reviews are available on each topic. For instance, monosomy of chromosome 3 and gain of 8q are often found in UMs. In addition, studies revealed that a mutation in the alpha subunit of the heterotrimeric G gene (GNAQ) was present in almost 50% of all UMs examined, and that UM metastatic spread was closely related to mutations in the BRCA associated protein 1 (BAP1) gene on chromosome 3 [5, 6]. However, more data is needed to elucidate the process of tumorigenesis of UM, which is currently still poorly characterized.
Compared with the genetic mechanisms involved in UMs, the role of epigenetics in carcinogenesis is less well defined. Recent studies propose that epigenetic alterations may be another hallmark of cancer due to their role in the initiation of carcinogenesis [7, 8]. Epigenetic changes can lead to cancer characteristics even in mutation-free cells. Epigenetic mechanisms include microRNA expression level variations, hypermethylation of tumor suppressor genes, hypomethylation of oncogenes, and histone modification patterns. In this review, we will discuss the role of epigenetics in UM tumorigenesis and the potential modes of therapy derived from this area of research.
Epigenetic mechanisms in UM
Recent research has shed light on the involvement of a class of noncoding RNAs, known as miRNAs, in UM. miRNAs are a class of short (17-22 nucleotides in length), endogenous, noncoding RNAs involved in the regulation of gene expression . Many miRNAs manifest differential expression levels in UM tissues and cell lines. By base-pairing with the complementary sites on the 3ʹ-untranslated region (3ʹUTR) of mRNAs, miRNAs regulate target genes by degrading mRNAs and repressing their translation . Several studies have reported that dysregulation of miRNAs can promote cell-cycle progression, confer resistance to apoptosis, and enhance invasiveness and metastasis of cancer cells. In a recent study, six miRNAs (let-7b, miR-199a, miR-199a*, miR-143, miR-193b and miR-652) were found to differentiate class 1 and class 2 UM tumors . Another study identified 19 miRNAs expressed in non-metastasizing melanoma were absent in metastasizing melanoma, and 11 miRNAs expressed in metastasizing melanoma were absent in non-metastasizing melanoma . Lori et al. used a microarray to analyze miRNA expression levels in UM with metastasis and found that let-7b and miRNA-199a showed high sensitivity and specificity for differentiation .
miR-34a: miR-34a inhibits the proliferation and migration of UM cells. Bioinformatic prediction suggested that the oncogene, c-Met, is a target of miR-34a in UM cells. Furthermore, miR-34a can down-regulate phosphorylated Akt (protein kinase B) and many cell cycle-related proteins .
miR-137: Chen et al. demonstrated that miR-137 expression was lower in UM cell lines than in benign uveal melanocytes . Functional analysis of miR-137 indicated that over-expression of miR-137 increased G1 cell cycle arrest, leading to a significant reduction in cell growth in UM. Ectopic transfection of miR-137 into UM cells down-regulated MITF, a transcription factor with oncogenic activity. In addition, over-expression of miR-137 down-regulated the oncogenic tyrosine kinase protein receptor c-Met and cell cycle-related proteins, including CDK6.
miR-149*: The miR-149* expression level has a statistically significant association with liver metastasis in UMs. Glycogen synthase kinase-3α (GSK-3α), a known gene target of miR-149*, encodes an important melanoma growth regulator .
miR-134: miR-134 is associated with invasiveness and metastasis in many other tumors with putative gene targets including the VEGFA, FOXM1, MYCN, CD9 and WWOX1 genes . Venkatesan et al. discovered a higher percentage of miR-134 (94.11%) in UM with liver metastasis than those without metastasis, irrespective of chromosome 3 aberrations, which suggests that miR-134 could be a potential biomarker for class 2 tumors .
Let 7b: Let 7b, a known tumor suppressor miRNA, is down-regulated in various cancers such as acute lymphoblastic leukemia and retinoblastoma [18, 19]. Restoration of let-7b is regarded as a potential therapeutic option in many cancers. Let-7 has also been demonstrated as a strong discriminator in primary UM, and has been reported at low levels in OCM1 cells [11, 20]. Research indicates that let-7b over-expression down-regulates cyclin D1 expression, which plays a critical role in cell cycle arrest, and enhances the radio-sensitivity of UM through cell cycle arrest .
miR-34b/c: Feng et al. discovered that miR-34b/c expression was dramatically decreased in 5 specimens in contrast to normal uveal tissues. The transfection of miR-34b/c into UM cells leads to a significant decrease in cell growth and metastasis. miR-34b/c caused cell cycle G1 arrest rather than the induction of apoptosis. Met proto-oncogene (c-Met) is considered a target of miR-34b/c in UM cells. Furthermore, miR-34b/c was confirmed to down-regulate the expression of p-Akt, and many cell cycle-related proteins .
Main functions of the dysregulated miRNAs in UM.
miR-182: miR-182 expression is dependent on p53 induction in UM cells. Interestingly, Yan et al. found that compared with normal uveal tissues, the expression of miR-182 was significantly decreased in tumor specimens. Transient transfection of miR-182 into cultured UM cells induced a significant decrease in cell growth, migration and invasiveness. Cells transfected with miR-182 manifested increased cell cycle G1 arrest and apoptotic activity. MITF, BCL2 and cyclin D2 are three potential target genes of miR-182. In addition, the expression of oncogene c-Met and its downstream Akt and ERK1/2 pathways are also down-regulated by miR-182 .
The detailed mechanisms of action of miRNAs in tumor development and progression are complex and numerous . However, most of them converge on common signaling pathways that govern cell proliferation, apoptosis and invasion . The significance of specific miRNAs in UM progression should be interpreted in appropriate biological backgrounds as miRNA interacts widely with other signaling cascades and often behaves diversely in different histological subtypes of UM. Population-based differences in miRNA dysregulation, and the diagnostic or prognostic use of miRNAs in different racial groups are also key considerations . Recent advances in the development of internal RNA delivery systems may open up new opportunities for the use of miRNAs as new cancer therapeutics . It is anticipated that, with a more comprehensive understanding of miRNAs and the associated abnormalities in cellular signaling in UM, novel therapeutics will emerge before long.
Long non-coding RNAs
Long non-coding RNAs (long ncRNAs, lncRNA) are non-protein coding transcripts longer than 200 nucleotides, which were initially considered to be the 'dark matter' of the genome. In recent years, the importance of the role played by lncRNAs on the regulation of gene expression has been increasingly recognized. Unlike miRNAs, lncRNAs display complex secondary and tertiary structures allowing them to bind vital proteins, RNA and DNA to carry out their regulatory functions . Accumulating evidence suggests that lncRNAs play important roles in a range of processes including transcriptional regulation, tumorigenesis and the metastatic cascade [32, 33]. For instance, the lncRNA Kcnq1ot1 forms chromatin loops to control genomic imprinting . Recent studies have also revealed that the CASC15 lncRNA was upregulated during melanoma progression and correlated with cell proliferation and invasion phenotypes of melanoma . In addition, our laboratory found that knockdown of lncRNA P2RX7-V3 expression in UM cells resulted in a cell growth defect, decreased invasion and a decreased rate of colony formation of melanoma cells. We further discovered that the PI3K-AKT signaling pathway served as a major target of P2RX7-V3. These data indicated that P2RX7-V3 plays a regulatory role in tumor progression and may serve as a new oncoRNA (manuscript in press).
Besides, lncRNAs can also work together with other epigenetic mechanisms, such as histone methylation and microRNAs, to modulate the cancer behaviors. Fan used epigenetic approaches to demonstrate that the lncRNA ROR acts as a necessary decoy oncogenic RNA (oncoRNA) that plays an important regulatory role in tumorigenesis of UM cells and colorectal cancer cells and represents a novel style of histone modification . Ding et al. discovered that lncRNA PAUPAR acted as a necessary UM suppressor and could silence HES1 expression, which significantly reduced metastasis. Mechanistically, PAUPAR inhibits histone H3K4 methylation to modulate HES1 expression . Lei demonstrated that lncRNA MALAT1 was upregulated in the uveal melanoma tissues and cell lines. The knockdown of MALAT1 suppressed the uveal melanoma cell proliferation, colony information, invasion and migration partly through modulating miR-140 expression .
Actually, lncRNAs sometimes play as a downstream target of cancer suppressors. LncRNA-numb was found to restore the function of HIC1 in UM cells, which is an important protein to modulate uveal melanoma progression. Overexpression of HIC1 led to the normal level of lncRNA-numb .
Researches in other noncoding RNAs like circRNA and ceRNA are getting more prevalent in many diseases such as Alzheimer's disease (AD), Hirschsprung's disease and cancers [40-42]. In the field of uveal melanoma, however, studies related with circRNAs could not be found so far and deep researches are necessary in the future.
Epigenetic modification of gene expression is an important mechanism in tumorigenesis, and may be reversed by specific treatment.
Abnormal promoter hyper-methylation of CpG islands is thought to play an important role in the inactivation of tumor suppressor genes (TSGs) in cancer .
p16INK4a(cyclin-dependent kinase inhibitor 2A): Previous studies have found that the loss of p16INK4A expression in patients with progressing melanoma is associated with increased tumor cell proliferation and decreased patient survival [44, 45]. Progression of tumor cells through the G1 phase of the cell cycle is stimulated by the association of cyclin D with cyclin-dependent kinases (CDKs) that phosphorylate Rb . Upon Rb phosphorylation, E2F is activated and enhances S-phase-specific gene expression. p16INK4a has been identified as an inhibitor of the cyclin D/CDK complex, as it can restrict the cyclin D-CDK4 and cyclin D-CDK6 kinases and result in cell cycle control at the G1-S restriction point. Although p16INK4a is commonly inactivated in a wide range of malignancies , germ-line mutations of p16 INK4a are uniquely associated with familial cutaneous melanoma instead of UM [49, 50]. An alternative mechanism for tumor suppressor gene inactivation is de novo methylation of CpG islands, which generally reduces transcription. De novo methylation of the p16INK4a promoter region occurs in a wide range of malignancies  and releases the cell from a potent cell cycle inhibitor. A recent study found that in both primary UM and UM cell lines, p16INK4a is frequently inactivated by hypermethylation, which is accompanied by down-regulated expression of p16 INK4a . This study also reported that loss of p16 INK4a expression, attributable to CpG methylation, could be reversed when treated with the demethylating drug 5-aza-2-deoxycytidine. Interestingly, metastasis tends to be more common in UM patients who possess a tumor with a methylated p16INK4a promoter, so aberrant methylation can be modulated and, hence, provides an effective target for the treatment of UM. Another study showed that epigenetic alterations in the p14ARF and p16INK4A genes were frequently associated with cutaneous as well as UMs, and they used ChIP experiments to clearly demonstrate that DNMT1 and DNMT3b played a dominant role in p16INK4A repression.
RASSF1A (RAS association domain family 1 isoform A): The RASSF1A promoter gene is known to be extremely common in cancers of the breast, head and neck, lung and cutaneous melanoma . It has been discovered that RASSF1A plays an important role in cell-cycle regulation, apoptosis and microtubule stability [54, 55]. The RASSF1A gene is located on chromosome 3p21.3, and its absence or inactivation has been shown to be a contributing factor in UM tumor formation and progression . One study showed that RASSF1A expression suppresses UM tumorigenesis and is frequently silenced in the UM-15 cell line and that re-expression of RASSF1A in UM-15 cells reverses the tumoral behavior, as demonstrated by a slower proliferation rate and restoration of sensitivity to cisplatin treatment . The RASSF1A gene contains two CpG islands, spanning the promoter and the first exon gene regions, which are susceptible to de novo methylation. Methylation of these sites blocks cell-cycle progression from G1 to S phase by controlling entry at the retinoblastoma check point and inhibiting cyclin D1 protein accumulation at the post-transcriptional level . Hypermethylation-induced loss of RASSF1A expression leads to a reduction in G1/S-phase cell-cycle control. In human mammary epithelial cells, RASSF1A dominates the oncogenic RAS effects, which means that loss of RASSF1A may be a determining step for oncogenic transformation in the absence of RAS-activating mutations. In addition, overexpression of RASSF1A enhances the formation of stable microtubules and blocks RAS-activated genomic instability, suggesting that the RASSF1A protein plays a potential role in the maintenance of spindle function and genomic stability . Loss of one copy of chromosome 3 (monosomy 3) has been reported in approximately half of all UMs and is related to the metastatic capacity of the tumor. Given the location of RASSF1A on the p21.3 region of chromosome 3, it might serve as a tumor suppressor gene whose silencing by methylation acts as a 'second hit' after monosomy occurs . Although the methylation of RASSF1A may not be considered wholly responsible for UM development, it could be a contributing factor in tumor formation and progression. This assumption is supported by a study showing that down-regulated expression of RASSF1A frequently occurs in primary UM . One study of reported a positive trend between DNA methylation and UM patients' survival . The same study also suggested that the methylation of RASSF1A protein is a potential tumor marker in UM.
RASEF (Ras and EF-hand domain-containing protein): Recently, segregate studies in families with uveal and cutaneous melanoma identified 9q21 as a potential locus harboring a tumor suppressor gene. One of the genes in this region, RASEF, was analyzed as a candidate tumor suppressor gene. The RASEF gene, also known as RAB45 or FLJ31614, is located on chromosome 9, region q21 . It encodes a protein with a calcium-binding EF-hand and Ras GTPase (Rab family) motif, which is potentially involved in the RAS pathway prominent in the development of melanoma . In a study by Maat et al., 11 UM cell lines and 35 primary UM samples were screened for mutations in the RASEF gene region by high-resolution melting-curve and digestion analysis. They found that all cell lines and samples that did not express RASEF contained a methylated promoter, whereas those with RASEF expression lacked this methylation. Furthermore, they demonstrated methylation not only coincided with low expression but also with a homozygous genotype, suggesting that a combination of methylation and loss of heterozygosity may be the mechanism for loss of expression . Additional effects of the loss of heterozygosity seem to be related to the aggressive behavior of the tumor, because homozygous tumors with a methylated RASEF promoter region tend to display decreased survival compared with heterozygous tumors without methylation (P=0.019).
Compared with DNA hypermethylation of tumor suppressor genes in tumorigenesis, DNA hypomethylation is less common. For instance, Preferentially Expressed Antigen in Melanoma (PRAME) is an accurate biomarker of metastasis in uveal melanoma . Field et al. found that specific CpG sites around the PRAME promoter are differentially hypomethylated. As a result, the gene is activated in Class 1 and Class 2 uveal melanomas and is associated with increased metastatic risk in both classes . Besides, a recent study discovered that 41/64 uveal melanomas (64.1%) showed higher expression of Deleted in Split hand/Split foot 1 (DSS1) gene than normal tissues. There was a significant association between high DSS1 expression levels and some clinicopathological features. An inverse correlation between DSS1 expression activity and methylation status of its promoter was verified, while DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine could significantly increase DSS1 expression in vitro .
Histone modification refers to the process of histone methylation, acetylation, phosphorylation, polyadenylation, ubiquitination and ADP ribosylation, carried out with assistance from the related enzyme.
Histone methylation: Post-translational methylation of histone lysine or arginine residues is real common and plays important roles in gene regulation. Aberrant histone methylation due to gene mutation, translocation, or overexpression can often lead to initiation of a cancer. For example, monomethylation of H4K20 and H2BK5; trimethylation of H3K4, H3K36 and H3K79 promote gene expression, whereas dimethylation of H3K9 and trimethylation of H3K9 and H3K27 inhibit gene expression [70, 71]. In UM cells, Holling et al. reported an association between impaired CIITA transcript levels and a high rate of trimethylated histone H3-lysine 27 (H3K27me3) in CIITA-PIV chromatin, rather than DNA methylation of MHC2TA promoter IV (CIITA-PIV). They demonstrated the presence of the histone methyltransferase EZH2 in CIITA-PIV chromatin, which is known to be a component of the polycomb repressive complex 2 and able to triple methylate histone H3-lysine 27 . In addition, transcription factor HES1 is overexpressed in UM cell lines and is associated with its metastatic capacity. And one of the reasons of upregulated expression of HES1 in UM cells is H3K4 trimethylation of the HES1 promoter .
Histone phosphorylation: Histone phosphorylation plays an important role in transcriptional activation and chromatin compaction during cell mitosis and meiosis . Especially, histone phosphorylation of H1, H2B, H3 has extensive functions in DNA repair and gene regulation . For example, Ser10 and Ser28 of H3 specifically at the promoter locus of FOS and JUN genes are often be phosphorylated by mitogen and stress-activated kinase 1 and 2 (MSK1/2) in tumors. This phenomenon is common in breast, prostate and colorectal cancers [75, 76]. Histone H3, phosphorylated at Ser28, is regarded as an M-phase protein marker. Zhang et al. found that in uveal melanoma, irradiated tumor cells showed G2 phase arrest as well as the high expression of histone H3 phosphorylated at Ser28, which could be reversed by knockdown of p21 .
Functional characterization of the methylated promoters in UM.
Histone acetylation: The balance between acetylation and deacetylation of a gene is determined by the relative activities of histone acetyltransferases and histone deacetylases (HDACs). Increased acetylation promotes greater chromatin accessibility for gene expression. For example, acetylation of H3K9 and H3K14 enhances gene expression . Studies suggest that down regulated expression of BAP1 led to impaired differentiation in UM cells. And this important function can be partially reversed by HDAC inhibitors, which can increase histone H3 acetylation .
Potential therapeutics targeting epigenetic regulators
Therapies targeting well-defined markers, such as overexpressed Her-2 in breast cancer and fused Bcr-abl in chronic myeloid leukemia, are often initially successful but falter when subpopulations of resistant cancer cells become dominant. Hence, the new paradigm of drug development is the targeting of multiple hallmarks of cancer simultaneously. Recent research has proven that epigenetics plays a role in the development of many cancers and strongly suggests that epigenetic mechanisms play an important role in the early diagnosis, treatment and prognosis of these tumors. Combining therapeutics targeting epigenetic regulators of cancer with traditional therapeutic strategies may offer great advantages. Exposure to epigenetic and non-epigenetic drugs that re-express tumor suppressor genes should enhance the efficiency of classical therapeutics of UM and sensitize the cancer cells to lower doses of traditional cytotoxic drugs .
In recent years, the potential clinical application of therapeutic methods aimed at epigenetic regulators have rapidly emerged. For example, miR-375 interference or destruction is a promising therapeutic avenue in the context of paclitaxel-resistant cervical cancer . Treatment with HDACi sensitizes breast and ovarian cancer cell lines to the calpeptin, TRAIL, and telomere homolog oligonucleotides . The demethylating agent, 5-azacitidine, sensitizes ovarian cancer cells to classical platinum-based chemotherapeutics . In addition, the prognosis of acute leukemia patients can be determined by measuring the hypermethylation level of CpG islands in the P15 gene. Along with advances in genomics methodology, researchers are uncovering abnormal DNA methylation patterns. This information can be applied to expression microarrays in their use as forecasting tools to predict cancer progression and prognosis. Such studies have been carried out for a number of tumor types and could potentially be applied to the diagnosis and prognosis of UM.
To date, no epigenetic drugs have been applied in clinical use for UM; however, this may change in the near future due to the emergence of a large number of new potential targets. MicroRNA is an important epigenetic regulatory system that may be targeted as a cancer therapy. Targeting specific miRNAs could be particularly effective in cancers in which miRNAs have been found to confer chemotherapeutic resistance. Zhou et al. found that let-7b could potentially be used as a radio-sensitivity enhancer in UM radiotherapy . miR-34b/c expression, which is dramatically reduced in UM cells and clinical samples, can be up-regulated by doxorubicin and epigenetic drugs. It is anticipated that novel therapeutics will emerge as miRNA dysregulation and the associated abnormalities in cellular signaling in UM become more comprehensively understood.
Another common epigenetic mechanism in UM generation is hypermethylation of some important gene promoters. A prerequisite for re-expression of epigenetically-silenced tumor suppressor genes is demethylation of the regulatory regions. DNA methyltransferase-1 (DNMT1) inhibitors, such as 5-azacitidine and its derivatives, are the most well-known demethylating agents . Chen et al. reported that a DNA hypomethylating agent, 5-aza-2ʹ-deoxycytidine, could increase the expression levels of miR-137, which may be epigenetically silenced during UM tumorigenesis . In addition, miR-124a expression could be regulated via epigenetic mechanisms, such as those involving the DNA hypomethylating agent, 5-aza-2'-deoxycytidine, or the histone deacetylase inhibitor, trichostatin A .
Epigenetics offers new promise for cancer therapeutics. Combining traditional therapies with novel epigenetic strategies may prove effective for the treatment of UM.
This review summarizes the currently available literature on the function of epigenetic alterations, particularly focusing on UM. Many epigenetic changes, including miRNA expression level variations, hypomethylation of oncogenes, hypermethylation of tumor suppressor genes and histone modification patterns, are known to be associated with UM tumorigenesis and many other cancers. Further studies are expected to elucidate how these variations are generated and, in turn, how they regulate the development and metastasis of cancer cells. An increased understanding of epigenetic mechanisms will not only be important in unraveling how cancer cells engender, transform and acquire resistance to chemotherapy and radiation, but will also be invaluable in the design of more potent epigenetic drugs. These treatments, in combination with traditional therapies, will permit accurate targeting of cancer cells and likely reduce the significant mortality associated with cancer relapse.
The authors have declared that no competing interest exists.
This work was supported by the Scientific Research Program of the National Health and Family Planning Commission of China (201402014), the National Natural Science Foundation of China (grants 81570884, U1432117, 81372469, 81372909), the SMC-ChenXing Yong Scholar Program (2016, Class A). The funders played no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
1. Yonekawa Y, Kim IK. Epidemiology and management of uveal melanoma. Hematol Oncol Clin North Am. 2012;26:1169-84
2. Prescher G, Bornfeld N, Hirche H, Horsthemke B, Jockel KH, Becher R. Prognostic implications of monosomy 3 in uveal melanoma. Lancet. 1996;347:1222-5
3. Collaborative Ocular Melanoma Study G. Assessment of metastatic disease status at death in 435 patients with large choroidal melanoma in the Collaborative Ocular Melanoma Study (COMS): COMS report no. 15. Arch Ophthalmol. 2001;119:670-6
4. Luke JJ, Callahan MK, Postow MA, Romano E, Ramaiya N, Bluth M. et al. Clinical activity of ipilimumab for metastatic uveal melanoma: a retrospective review of the Dana-Farber Cancer Institute, Massachusetts General Hospital, Memorial Sloan-Kettering Cancer Center, and University Hospital of Lausanne experience. Cancer. 2013;119:3687-95
5. Onken MD, Worley LA, Long MD, Duan S, Council ML, Bowcock AM. et al. Oncogenic mutations in GNAQ occur early in uveal melanoma. Investigative ophthalmology & visual science. 2008;49:5230-4
6. Van Raamsdonk CD, Bezrookove V, Green G, Bauer J, Gaugler L, O'Brien JM. et al. Frequent somatic mutations of GNAQ in uveal melanoma and blue naevi. Nature. 2009;457:599-602
7. Venza M, Visalli M, Biondo C, Oteri R, Agliano F, Morabito S. et al. Epigenetic marks responsible for cadmium-induced melanoma cell overgrowth. Toxicology in vitro: an international journal published in association with BIBRA. 2015;29:242-50
8. Venza M, Visalli M, Beninati C, Biondo C, Teti D. Role of genetics and epigenetics in mucosal, uveal, and cutaneous melanomagenesis. Anti-cancer agents in medicinal chemistry. 2015
9. Fu LL, Zhao X, Xu HL, Wen X, Wang SY, Liu B. et al. Identification of microRNA-regulated autophagic pathways in plant lectin-induced cancer cell death. Cell Prolif. 2012;45:477-85
10. Wang Z, Yin B, Wang B, Ma Z, Liu W, Lv G. MicroRNA-210 promotes proliferation and invasion of peripheral nerve sheath tumor cells targeting EFNA3. Oncol Res. 2013;21:145-54
11. Worley LA, Long MD, Onken MD, Harbour JW. Micro-RNAs associated with metastasis in uveal melanoma identified by multiplexed microarray profiling. Melanoma research. 2008;18:184-90
12. Radhakrishnan A, Badhrinarayanan N, Biswas J, Krishnakumar S. Analysis of chromosomal aberration (1, 3, and 8) and association of microRNAs in uveal melanoma. Molecular vision. 2009;15:2146-54
13. Yan D, Zhou X, Chen X, Hu DN, Dong XD, Wang J. et al. MicroRNA-34a inhibits uveal melanoma cell proliferation and migration through downregulation of c-Met. Investigative ophthalmology & visual science. 2009;50:1559-65
14. Chen X, Wang J, Shen H, Lu J, Li C, Hu DN. et al. Epigenetics, microRNAs, and carcinogenesis: functional role of microRNA-137 in uveal melanoma. Investigative ophthalmology & visual science. 2011;52:1193-9
15. Venkatesan N, Kanwar J, Deepa PR, Khetan V, Crowley TM, Raguraman R. et al. Clinico-Pathological Association of Delineated miRNAs in Uveal Melanoma with Monosomy 3/Disomy 3 Chromosomal Aberrations. PloS one. 2016;11:e0146128
16. Madhunapantula SV, Sharma A, Gowda R, Robertson GP. Identification of glycogen synthase kinase 3alpha as a therapeutic target in melanoma. Pigment Cell Melanoma Res. 2013;26:886-99
17. Liu CJ, Shen WG, Peng SY, Cheng HW, Kao SY, Lin SC. et al. miR-134 induces oncogenicity and metastasis in head and neck carcinoma through targeting WWOX gene. International journal of cancer Journal international du cancer. 2014;134:811-21
18. Mi S, Lu J, Sun M, Li Z, Zhang H, Neilly MB. et al. MicroRNA expression signatures accurately discriminate acute lymphoblastic leukemia from acute myeloid leukemia. Proc Natl Acad Sci U S A. 2007;104:19971-6
19. Danda R, Krishnan G, Ganapathy K, Krishnan UM, Vikas K, Elchuri S. et al. Targeted expression of suicide gene by tissue-specific promoter and microRNA regulation for cancer gene therapy. PloS one. 2013;8:e83398
20. Venza M, Dell'Aversana C, Visalli M, Altucci L, Teti D, Venza I. Identification of microRNA expression patterns in cutaneous and uveal melanoma cell lines. Tumori. 2014;100:e4-7
21. Zhou Y, Zhang L, Fan J, Jia R, Song X, Xu X. et al. Let-7b overexpression leads to increased radiosensitivity of uveal melanoma cells. Melanoma research. 2015;25:119-26
22. Dong F, Lou D. MicroRNA-34b/c suppresses uveal melanoma cell proliferation and migration through multiple targets. Molecular vision. 2012;18:537-46
23. Yan D, Dong XD, Chen X, Yao S, Wang L, Wang J. et al. Role of microRNA-182 in posterior uveal melanoma: regulation of tumor development through MITF, BCL2 and cyclin D2. PloS one. 2012;7:e40967
24. Yang H, Kong W, He L, Zhao JJ, O'Donnell JD, Wang J. et al. MicroRNA expression profiling in human ovarian cancer: miR-214 induces cell survival and cisplatin resistance by targeting PTEN. Cancer research. 2008;68:425-33
25. Xu CX, Xu M, Tan L, Yang H, Permuth-Wey J, Kruk PA. et al. MicroRNA MiR-214 regulates ovarian cancer cell stemness by targeting p53/Nanog. The Journal of biological chemistry. 2016;291:22851
26. Dror R, Lederman M, Umezawa K, Barak V, Pe'er J, Chowers I. Characterizing the involvement of the nuclear factor-kappa B (NF kappa B) transcription factor in uveal melanoma. Investigative ophthalmology & visual science. 2010;51:1811-6
27. Liu HS, Xiao HS. MicroRNAs as potential biomarkers for gastric cancer. World J Gastroenterol. 2014;20:12007-17
28. Banaudha KK, Verma M. The role of microRNAs in the management of liver cancer. Methods Mol Biol. 2012;863:241-51
29. Wang J, Wang Q, Liu H, Hu B, Zhou W, Cheng Y. MicroRNA expression and its implication for the diagnosis and therapeutic strategies of gastric cancer. Cancer Lett. 2010;297:137-43
30. Li X, Yang W, Lou L, Chen Y, Wu S, Ding G. microRNA: a promising diagnostic biomarker and therapeutic target for hepatocellular carcinoma. Dig Dis Sci. 2014;59:1099-107
31. Botti G, Marra L, Malzone MG, Anniciello A, Botti C, Franco R. et al. LncRNA HOTAIR as prognostic circulating marker and potential therapeutic target in patients with tumor diseases. Curr Drug Targets. 2015
32. Liu Q, Huang J, Zhou N, Zhang Z, Zhang A, Lu Z. et al. LncRNA loc285194 is a p53-regulated tumor suppressor. Nucleic Acids Res. 2013;41:4976-87
33. Im JH, Muschel RJ. New evidence of lncRNA role in tumor progression and metastasis. Hepatobiliary Surg Nutr. 2012;1:55-6
34. Zhang H, Zeitz MJ, Wang H, Niu B, Ge S, Li W. et al. Long noncoding RNA-mediated intrachromosomal interactions promote imprinting at the Kcnq1 locus. J Cell Biol. 2014;204:61-75
35. Lessard L, Liu M, Marzese DM, Wang H, Chong K, Kawas N. et al. The CASC15 Long Intergenic Noncoding RNA Locus Is Involved in Melanoma Progression and Phenotype Switching. J Invest Dermatol. 2015;135:2464-74
36. Fan J, Xing Y, Wen X, Jia R, Ni H, He J. et al. Long non-coding RNA ROR decoys gene-specific histone methylation to promote tumorigenesis. Genome Biol. 2015;16:139
37. Ding X, Wang X, Lin M, Xing Y, Ge S, Jia R. et al. PAUPAR lncRNA suppresses tumourigenesis by H3K4 demethylation in uveal melanoma. FEBS Lett. 2016;590:1729-38
38. Sun L, Sun P, Zhou QY, Gao X, Han Q. Long noncoding RNA MALAT1 promotes uveal melanoma cell growth and invasion by silencing of miR-140. Am J Transl Res. 2016;8:3939-46
39. Cheng G, He J, Zhang L, Ge S, Zhang H, Fan X. HIC1 modulates uveal melanoma progression by activating lncRNA-numb. Tumour biology: the journal of the International Society for Oncodevelopmental Biology and Medicine. 2016;37:12779-89
40. Xu L, Zhang M, Zheng X, Yi P, Lan C, Xu M. The circular RNA ciRS-7 (Cdr1as) acts as a risk factor of hepatic microvascular invasion in hepatocellular carcinoma. J Cancer Res Clin Oncol. 2016
41. Zhao Y, Alexandrov PN, Jaber V, Lukiw WJ. Deficiency in the Ubiquitin Conjugating Enzyme UBE2A in Alzheimer's Disease (AD) is Linked to Deficits in a Natural Circular miRNA-7 Sponge (circRNA; ciRS-7). Genes (Basel). 2016:7
42. Peng L, Chen G, Zhu Z, Shen Z, Du C, Zang R. et al. Circular RNA ZNF609 functions as a competitive endogenous RNA to regulate AKT3 expression by sponging miR-150-5p in Hirschsprung's disease. Oncotarget. 2016
43. Weisenberger DJ, Siegmund KD, Campan M, Young J, Long TI, Faasse MA. et al. CpG island methylator phenotype underlies sporadic microsatellite instability and is tightly associated with BRAF mutation in colorectal cancer. Nat Genet. 2006;38:787-93
44. Straume O, Smeds J, Kumar R, Hemminki K, Akslen LA. Significant impact of promoter hypermethylation and the 540 C>T polymorphism of CDKN2A in cutaneous melanoma of the vertical growth phase. Am J Pathol. 2002;161:229-37
45. Straume O, Sviland L, Akslen LA. Loss of nuclear p16 protein expression correlates with increased tumor cell proliferation (Ki-67) and poor prognosis in patients with vertical growth phase melanoma. Clin Cancer Res. 2000;6:1845-53
46. Draetta GF. Mammalian G1 cyclins. Curr Opin Cell Biol. 1994;6:842-6
47. Serrano M, Hannon GJ, Beach D. A new regulatory motif in cell-cycle control causing specific inhibition of cyclin D/CDK4. Nature. 1993;366:704-7
48. Sharpless NE, DePinho RA. The INK4A/ARF locus and its two gene products. Curr Opin Genet Dev. 1999;9:22-30
49. Harland M, Meloni R, Gruis N, Pinney E, Brookes S, Spurr NK. et al. Germline mutations of the CDKN2 gene in UK melanoma families. Hum Mol Genet. 1997;6:2061-7
50. Hughes-Davies TH. CDKN2A mutations in multiple primary melanomas. N Engl J Med. 1998;339:347-8
51. Baylin SB, Herman JG. DNA hypermethylation in tumorigenesis: epigenetics joins genetics. Trends Genet. 2000;16:168-74
52. van der Velden PA, Metzelaar-Blok JA, Bergman W, Monique H, Hurks H, Frants RR. et al. Promoter hypermethylation: a common cause of reduced p16(INK4a) expression in uveal melanoma. Cancer research. 2001;61:5303-6
53. Pfeifer GP, Yoon JH, Liu L, Tommasi S, Wilczynski SP, Dammann R. Methylation of the RASSF1A gene in human cancers. Biol Chem. 2002;383:907-14
54. Agathanggelou A, Cooper WN, Latif F. Role of the Ras-association domain family 1 tumor suppressor gene in human cancers. Cancer research. 2005;65:3497-508
55. Spugnardi M, Tommasi S, Dammann R, Pfeifer GP, Hoon DS. Epigenetic inactivation of RAS association domain family protein 1 (RASSF1A) in malignant cutaneous melanoma. Cancer research. 2003;63:1639-43
56. Maat W, van der Velden PA, Out-Luiting C, Plug M, Dirks-Mulder A, Jager MJ. et al. Epigenetic inactivation of RASSF1a in uveal melanoma. Investigative ophthalmology & visual science. 2007;48:486-90
57. Dratviman-Storobinsky O, Cohen Y, Frenkel S, Merhavi-Shoham E, El SD, Binkovsky N. et al. The role of RASSF1A in uveal melanoma. Investigative ophthalmology & visual science. 2012;53:2611-9
58. Shivakumar L, Minna J, Sakamaki T, Pestell R, White MA. The RASSF1A tumor suppressor blocks cell cycle progression and inhibits cyclin D1 accumulation. Mol Cell Biol. 2002;22:4309-18
59. Vos MD, Martinez A, Elam C, Dallol A, Taylor BJ, Latif F. et al. A role for the RASSF1A tumor suppressor in the regulation of tubulin polymerization and genomic stability. Cancer research. 2004;64:4244-50
60. Calipel A, Abonnet V, Nicole O, Mascarelli F, Coupland SE, Damato B. et al. Status of RASSF1A in uveal melanocytes and melanoma cells. Molecular cancer research: MCR. 2011;9:1187-98
61. Sweetser DA, Peniket AJ, Haaland C, Blomberg AA, Zhang Y, Zaidi ST. et al. Delineation of the minimal commonly deleted segment and identification of candidate tumor-suppressor genes in del(9q) acute myeloid leukemia. Genes Chromosomes Cancer. 2005;44:279-91
62. Shintani M, Tada M, Kobayashi T, Kajiho H, Kontani K, Katada T. Characterization of Rab45/RASEF containing EF-hand domain and a coiled-coil motif as a self-associating GTPase. Biochemical and biophysical research communications. 2007;357:661-7
63. Maat W, Beiboer SH, Jager MJ, Luyten GP, Gruis NA, van der Velden PA. Epigenetic regulation identifies RASEF as a tumor-suppressor gene in uveal melanoma. Investigative ophthalmology & visual science. 2008;49:1291-8
64. Field MG, Decatur CL, Kurtenbach S, Gezgin G, van der Velden PA, Jager MJ. et al. PRAME as an Independent Biomarker for Metastasis in Uveal Melanoma. Clin Cancer Res. 2016;22:1234-42
65. Field MG, Durante MA, Decatur CL, Tarlan B, Oelschlager KM, Stone JF. et al. Epigenetic reprogramming and aberrant expression of PRAME are associated with increased metastatic risk in Class 1 and Class 2 uveal melanomas. Oncotarget. 2016
66. Venza M, Visalli M, Catalano T, Beninati C, Teti D, Venza I. DSS1 promoter hypomethylation and overexpression predict poor prognosis in melanoma and squamous cell carcinoma patients. Hum Pathol. 2016
67. Voelter V, Diserens AC, Moulin A, Nagel G, Yan P, Migliavacca E. et al. Infrequent promoter methylation of the MGMT gene in liver metastases from uveal melanoma. International journal of cancer Journal international du cancer. 2008;123:1215-8
68. Venza M, Visalli M, Catalano T, Fortunato C, Oteri R, Teti D. et al. Impact of DNA methyltransferases on the epigenetic regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor expression in malignant melanoma. Biochemical and biophysical research communications. 2013;441:743-50
69. van den Bosch T, Koopmans AE, Vaarwater J, van den Berg M, de Klein A, Verdijk RM. Chemokine receptor CCR7 expression predicts poor outcome in uveal melanoma and relates to liver metastasis whereas expression of CXCR4 is not of clinical relevance. Investigative ophthalmology & visual science. 2013;54:7354-61
70. Li B, Carey M, Workman JL. The role of chromatin during transcription. Cell. 2007;128:707-19
71. Rosenfeld JA, Wang Z, Schones DE, Zhao K, DeSalle R, Zhang MQ. Determination of enriched histone modifications in non-genic portions of the human genome. BMC Genomics. 2009;10:143
72. Holling TM, Bergevoet MW, Wilson L, Van Eggermond MC, Schooten E, Steenbergen RD. et al. A role for EZH2 in silencing of IFN-gamma inducible MHC2TA transcription in uveal melanoma. Journal of immunology. 2007;179:5317-25
73. Fraga MF, Ballestar E, Villar-Garea A, Boix-Chornet M, Espada J, Schotta G. et al. Loss of acetylation at Lys16 and trimethylation at Lys20 of histone H4 is a common hallmark of human cancer. Nat Genet. 2005;37:391-400
74. Zhang K, Dent SY. Histone modifying enzymes and cancer: going beyond histones. J Cell Biochem. 2005;96:1137-48
75. Drobic B, Perez-Cadahia B, Yu J, Kung SK, Davie JR. Promoter chromatin remodeling of immediate-early genes is mediated through H3 phosphorylation at either serine 28 or 10 by the MSK1 multi-protein complex. Nucleic Acids Res. 2010;38:3196-208
76. Forbes SA, Beare D, Gunasekaran P, Leung K, Bindal N, Boutselakis H. et al. COSMIC: exploring the world's knowledge of somatic mutations in human cancer. Nucleic Acids Res. 2015;43:D805-11
77. Zhang XR, Liu YA, Sun F, Li H, Lei SW, Wang JF. p21 is Responsible for Ionizing Radiation-induced Bypass of Mitosis. Biomed Environ Sci. 2016;29:484-93
78. Barski A, Cuddapah S, Cui K, Roh TY, Schones DE, Wang Z. et al. High-resolution profiling of histone methylations in the human genome. Cell. 2007;129:823-37
79. Landreville S, Agapova OA, Matatall KA, Kneass ZT, Onken MD, Lee RS. et al. Histone deacetylase inhibitors induce growth arrest and differentiation in uveal melanoma. Clin Cancer Res. 2012;18:408-16
80. Sarkar S, Goldgar S, Byler S, Rosenthal S, Heerboth S. Demethylation and re-expression of epigenetically silenced tumor suppressor genes: sensitization of cancer cells by combination therapy. Epigenomics. 2013;5:87-94
81. Shen Y, Wang P, Li Y, Ye F, Wang F, Wan X. et al. miR-375 is upregulated in acquired paclitaxel resistance in cervical cancer. Br J Cancer. 2013;109:92-9
82. Sarkar S, Faller DV. T-oligos inhibit growth and induce apoptosis in human ovarian cancer cells. Oligonucleotides. 2011;21:47-53
83. Matei DE, Nephew KP. Epigenetic therapies for chemoresensitization of epithelial ovarian cancer. Gynecol Oncol. 2010;116:195-201
84. Chen X, He D, Dong XD, Dong F, Wang J, Wang L. et al. MicroRNA-124a is epigenetically regulated and acts as a tumor suppressor by controlling multiple targets in uveal melanoma. Investigative ophthalmology & visual science. 2013;54:2248-56
Corresponding authors: Shengfang Ge or Renbing Jia. geshengfangedu.cn or jrb19760517com